Well, how about figuring out what is wrong then? I have a few suggestions:
1. The GPU overheats (download HWMonitor and check temps when playing)
2. Check your RAM and VRAM usage when playing
3. The reason for the GPU overheating could be if the fans are broken or a shitty airflow
4. It could be that while installing the GPU you broke something else?
5. CPU could be bottlenecking. You can see this in HWMonitor. If your CPU is at 100% and the GPU is not on 100%, it is a bottleneck.
6. Update drivers and remove the old ones